Radio apparatus



June 21, 1932. R. MAURER- 1,863,909

RADIO APPARATUS Filed Jan. 25, 1930 2 Sheets-Sheet l lNVENTOR Passe; L. Medea:

June 21, 1932. MAURER 1,863,909

RADIO APPARATUS Filed Jan 25, 1930 2 Sheets-Sheet 2 IIIHIIIIIlllllIllllllllIlllllIIIIllllllllllillllllllIllIllllllllllllllllllllllllllllllllllllIlllll'llnll'll VIIIllIIllllllllllllllllllllllllllllllllllllllllIllllllll|||IIlllllllllllllllllllllllIllllllll if V r i \mm W -2 mm INVENTOR.

P1555 A. M

TTORNEYS.

Patented June 21, 1932 UNITED STATES. PATENT OFFICE RUSSELL L. MAUIt-ER, OF CHICAGO, ILLINOIS, ASSIGNOR TO GRIGSBY-GRUNOW COM PANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS RADIO APPARATUS Application filed January '25, 1930. Serial No. 423,468.

This invention relates to radio apparatus, and particularly to a combined radio and electric phonograph. It is customary to combine in one cabinet a radio receiving set with an electric phonograph so that the amplifier, speaker and power unit necessary forboth are common. A changeover switch is provided for selectively rendering the radio or phonograph portion of the unit operative. In order to makesuch-a combined unit as simple as possible to manufactureand operate, it is desirable that the controls therefor be reduced to the fewest number. Thus, the control of volume is essential for both radio and phonograph, and while each volume control for efficient operation is electrically and functionally distinct in the two systems, they are objectively the same.

In prior systems of this chacacter, it has been customary to dispose the phonograph volume control adjacent the turn-table and pick-up, both of which are usually in a closed compartment. This is objectionable for several reasons. In actual use itis difiicult to satisfactorily adjust the volume because with the cover of the cabinet raised to open the phonograph compartment, the unavoidable buzzing and mechanical reproduction from the parts of the pick-up add to the volume reproduced and tend to make the volume appear greater than when the cover is closed. Furthermore, if all the apparatus, such as transformers, vacuum tubes, and the like, are housed in a compact unit, it may be necessary to run a large number of leads'between theapparatus proper and the pick-up.

In order to reduce the number of controls to aminimum, Ihave .disposedthe volume control for both the radio and phonograph in such a-manner that one single knob located on the control panel is sufficient. F urthermore, the changeover switch usually provided is disposed on the same shaft as the volume control, thus rendering the, operation of changing, over from one to the other and controlling the Volume exceedingly simple.

The advantage of such a constructionlies in the fact that the number of control elements is reduced to a minimum, thus presenting a very simple control panel, and also permitting of the control of the phonograph reproduction with the cabinet cover down) In this way, the volume maybe controlledunder actual reproducing conditionswith the cover down tomuiiie needle and pick-up noise. By disposing the changeover switch and volume control in this manner, it is possible to start the record going with the pick-up on it,close the cover down, switch'the phonograph on and controlthe volume without hearingthe usual scratch, audible when the cover is raised. Y

Referring to the drawings: Fig. 1 is a diagrammatic representation of a 7 combined radio and phonographembodying my invention; and r v F 2 is a view showing a combined radio and electric phonograph in a cabinet;

The radio receiving portion ofthe system is well known and comprises two. antenna connecting terminals 1 and 2, connected to each other through a condenser 3. The antenna con-nections are provided with alead 4, from which an inductance 5 and condenser 6 are connected to ground. The junction point of 5 and 6 is connected toanothen in ductance 7, one end of which is connected to a variable tuning condenser 8, the other side of which is grounded. Junction point 10 of inductance 7 and condenser 8 is connected to the grid 12 ofthe vacuumtube 13.

Anode 14 of tube 13 is connectedthrough the primary 15 of a radio frequency transformer 16, a radio frequency choke 17 and terminal 18- of the positive pole of a power 2 supply (not shown). One side of secondary 17of radio frequency transformer 16 is con: nected through a balancing coil 20-to ground. The other side of secondary 17 is connected to thegrid of the succeeding amplifiertube. A trimming condenser '18 and tuning condenser 19 are shunted acrosssecondary'17' and balancing, coil 20. The junction of balancing coil 20' and secondary 17' isconneeted by neutralizing condenser 21, back' tothe grid of tube 13. Three additional similar stages of radiovfrequency amplifiers 25, 26 and 27 are shown similarly connected. The output of amplifier27'is'conducted to grid 28 of a detector tube 29 by means of leads,

30, 31, switch contact 32 of a changeover switch, lead 33, switch contact 34, leads 35 and 36. r

The output of the detector tube 29 is led to a radio frequency transformer choke 31, to the primary of an audio-frequency transformer 32, and then through leads 33, 34;, switch contact 35, lead 36, switch contact 37 and lead 38, to terminal 39 for connection to a suitable source of power supply. The secondary of audio-frequency transformer 32 is connected to a pair of amplifiers 40 and 41 arranged in push-pull relation in wellknown manner, and feeding into an output transformer 42. The output of transformer 42 maybe connected to a suitable loud speaker. (not shown). I

To energize the plate circuit of amplifiers 40 and 41, a lead from the center of the primary of transformer 42 is brought to terminal 43 for connection to the positive pole of a suitable source of current. The usual ground'connections are provided. The negative poles of the plate potential sources are grounded. v

.As clearly indicated, filaments 45 of the radio frequency amplifiers and detector are connected through suitable leads to terminals 46 adapted to be connected to a source of current. A resistance 47 having its center grounded is connected across posts 46, while a lamp 48 may be connected thereacross to illuminate the instrument panel. Filaments 50 of theaudio-frequency amplifier are connected by suitable leads to terminals 51 for connection to current supply. The equi-potential cathodes 52, 53, 54, 55 and 56 of the radio frequency amplifier and detector are connected through leads and condensers to ground.

It will be noted that the grids of all the amplifiers and detector are grounded. By impressing suitable potentials across ground and terminals 39 and 18, desired plate potentials will be established in the various tubes. By inserting biasing resistance between each cathode and ground, the drop in potential due to the passage of the plate current through the resistance will establish a desired grid bias at each tube. Audio amplifiers 40 and 41 are biased byconnecting a resistance 101 across the filament and grounding the center.

In order to control the volume of theradio receiving set, the potential of the cathodes of the radio frequency amplifiers with respectto ground may be varied, thus eifec tively changing the grid bias. In order to do this, rheostats 60 and 61 are provided. Rheostat '61 is preferably varied in accordance with the variation of the tuning condensers in each radio frequency, as disclosed in the co-pending application of M. W. Kenney, Serial No. 361,847, filed May 5, 1929; to provide substantially constant sensitivity at various frequencies. Rheostat 60 is varied by a knob 62 on shaft 63 to control the volume at any one frequency.

The electric phonograph is diagrammatically represented by a pick-up unit connected by suitable leads to a potentiometer 76. A contact member 77 may be connected to potentiometer 76 to control the volume of the pick-up unit. Contact member 77 is connected'by a lead 78 to the mid-point of an auto-transformer 80. One end of this transformer is grounded, while the other end is connected to switch point 81 of the changeover switch. The arms connecting'the various switch points of this changeover switch are shown in full lines when the radio set is operative. In order to operate the changeover switch, a lever 82 may be used.

IVhen thephonograph is turned on, the output of radio frequency amplifier 27 is short-circuited by lever 82 at switch point 83 to ground, while detector 29 becomes a stage of audio-frequency amplification. This is accomplished by connecting the auto-transformer through switch point 81, lead 85,

switch point 83, lead 87, and lead 36 to the grid of tube 28. Cathode 56 of tube 29 is connected through a fixed resistance and switch point 91, lead 92, to ground when the radio set isin operation. Upon the switching over to the phonograph, however, a different fixed resistance is connected at switch point 96 between ground and grid 28, thus impressing a different grid potential on tube 29.

Lead 33 in the connected through switch points 99 and 100 to terminal 18, thus changing the anode potential.

At the same time, cathode 55 of amplifier 27 which is grounded through its biasing resistance 98 to point 97 of the switch during the operation of the radio, has the ground broken when the phonograph is operated. This breaks the anode cathode circuit and prevents excessive plate current through the tube when the transformer is short-circuited.

Potentiometer 26, controlling the output of pick-up 7 5 may have its rotating member 77 mounted on the same shaft 63 operated by knob 62. In this way, it is evident that irrespective of the condition of the changeover switch, the operator of a combination set may control the speaker volume by means of a single knob.

In Fig. 2 is shown a combined radio and phonograph combination. A cabinet 100 of any desired design is provided with a motorboard 101 carrying a turn-table 102 and provided with a pick-up 103 mounted on an arm 1 5 104. A cover 105 is provided for closing the compartment. In front of the cabinet is a control panel 106 provided with control knobs 62, 107 and 108. Knob 107 has associated plate circuit of tube 29 is therewith a movable scale 109 set in an escutcheon plate 110. A grille 111 is provided for the loud speaker.

Since the volume of both the radio and phonograph is controlled by knob 62, it is evident that satisfactory volume adjustment may be made with cover closed. By having changeover switch handle 82 coaxial with knob 62, a simple control panel is obtained, making for effective control of the combination.

What I claim is:

A radio and electric phonograph combination comprising individual volume controls for the radio and phonograph portions of the combination, a changeover switch for selectively rendering one of said portions operative, a shaft for controlling both of said volume controls, said shaft adapted to project through a panel and being provided with a knob at the free end thereof for operation, a lever mounted for oscillation around said shaft and equally accessible with the volume control knob, and means connecting said lever and said changeover switch.

In testimony whereof he afiixes his signature.

RUSSELL L. MAUBER. 

